Cathode ray tube



July 16, i940.

F. R. BENEDICJT CATHODE RAY TUBE Filed Aug. 17, 193s 7 2 m N Wm ii TNQ 2 i NL 'ATTbRN Patented July 16, 1940 PATENT Noi-FICE cA'rnonE. RAY TUBE Frank R. Benedict, Pittsburgh, Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,

Pennsylvania a corporation of Application August 17, 1938, serial No. 225,355 h h a claims; (o1. 25o-27.5) l .y

My invention relates to cathode-ray tubes, and especially to the cathode assembly thereof.

An object of my invention is to provide Van intense and well concentrated cathode beam for the recording of high speed phenomena.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the drawing, in which:

Figure l is a view in cross-section of the main anode-cathode assembly `of a cathode-ray tube disclosing my invention;

Fig. 2 is a view mainly in elevation and partly in cross-section of a preferred type of cathoderay tube in which my inventionis embodied; and

Fig. 3 is a graph disclosing the potential gradient between the cathode and anode of a cathode ray tube.

For the recording of very high speed phenomena with the cathode-ray oscillograph, it is important 'that an intense and well concentrated cathode beam be obtained. In the prior art, the problem of the concentration of a beam has been considered as a problem of anode structure and various modiiications of the anode structure have been devised to concentrate the beam. My invention, on the other hand, contemplates designing the cathode structure so that the equipotential lines of force adjacent the active surface of the cathode will be convex toward this cathode surface, with the result that the particles emitted from the surface will be initially concentrated due to the lens-like action of these concave electric lines of force.

In Figure 1, I have disclosed a tube I0 preferably of glass or quartz, having the cathode structure II extending therein preferably through a cap I2. This cap I2 is secured to a ring I3 surrounding the glass tube I0, and the cap I2 and ring i3 are attached to one another, preferably by a screw-threaded joint I4 that comprises suitable sealing material, such as rubber washers I5, to protect the desired vacuum inside the glass tube Iii from the atmosphere.

The cathode assembly comprises a central metal member, such as the rod I6, having an active face Il and a shaft extending through the cap I2 to an outer cap I8. The cap I8 is secured to the shaft of the rod I6 and also has a screwthreaded connection I9 with the cap I2 for adjusting the position of the active face I1`within the glass tube I0. Bellows 2U surround the shaft of the rod I6 between the cap I2 and the cap I3. The rod IB is of metal having a low work function that will provide the particles for the cathode ray beam from the active face I1. The

material of this rod IB is preferably of aluminum or aluminummagnesium alloys orvother suitable materials having a low work function.

`Surrounding the rod I6 within the glass tube IIJ is a cylinder 2| of a metal having a higher '5 work function than that of the rod I6. This material is preferably that of stainless steel, al-

though other materials with a high work constant function could be used, such as nickel, brass, copper, platinum, silver, gold, etc. This cylindrical '10 member 2I may be attached to the inner part of tlezcap l2 by a screw-threaded joint as disclosed The cylinder 2| has a rounded lip or edge 23 that extends beyond the active face I1 of the 15 rod I6. In between the lip 23 and the active face I1 of the rod I6, the material is removed as shown at 24. yI have disclosed this space 24 as being countersunk with the rod I6 projecting therethrough. If desired, the shape of the face of the perforated cylinder 2l may be concave with the face I'I of the rod I6 above the central portion of the concave face. The active face I'I may be concave also although preferably to a slight extent.

Adjusting nuts 25 are disclosed for centering the glass tube I0 about the cathode structure. At the lower part of Fig. 2 is disclosed the metal tube 26 attached to the main anode 21 having a small perforated opening at 28 that becomes slightly larger at 29 for the emergence of the cathode beam.

In Fig. 2 is illustrated the type of cathode-ray tube to which my invention particularly applies. The members previously described in connection with Fig. 1 are disclosed in the upper part of Fig. 2, together with a casing 30 surrounding the major portion of the tube I 0. Various connections, such as 4 I, may be made through insulation 42 to magnetic coils or to auxiliary electrodes within the casing. Screws 43 may be connected through the casing for the adjustment of other auxiliary electrodes. Connections 44 preferably extend through insulating bushings in the casing to electrostatic deflecting plates. The observation screen is a fluorescent plate 45 shown in dotted lines, viewed from a window 46. A film may be exposed by operating a shutter mechanism 4l.

The lower end of the device is closed by a plate 48 by means of bolts 49. I

In Fig. 3, I have disclosed the potential gradient extending from the cathode structure to the main anode 21. It will be noted that nearly all of the major potential drop appears across the spaceadjacent the cathode, which is known Aas eld 'shape of the cathode. I have already described my preferred cathode structure in which `the active face I1 of the rod I6 is With-drawn in a plane away from the plane of the edge 23 of the cylinder 2l surrounding the rod li buty is above the central portion of the cylinder 2 l. The result of this Withdrawal is a concave shape to the equi-potential lens in the space adjacentthe cathodeface. Thisconcave formation of the lines of force is illustrated at 513 and 5! by dotted lines. beam will be emitted from the active face H,

and these concave equi-potential lines of force will act like a lens `to concentrate the beam on a line of the axis of the rod I6, as shown by the dotted lines 52. The result of this concentration Will be to impinge the beam Within the hole 28 instead of spreading it out over the surface of the anodeZl, and then concentrating a portion of it through the opening 2Q as in the prior art.

As illustrative and not limiting, I prefer to utilize the yglass tube lli` with about one inch inside diameter and about l5 inches long. The rod I6' is about 1A; inch in diameter and the cylindrical member 2l is preferably 5A; inch in diameter with the lips 23 having rounded edges of about le inch in thickness. The active face l 'l of the cathode is preferably about '70 mils back of the plane ofthe rounded ends 23. The adjustment of the cap I8 is particularly valuable with the Wearv of the face il after the oscillograph The particles forming the cathode-ray 2,208,406 the Crookes dark space. My invention conternhas been used for some time. Theadjustment `will bring theactive face to the ybest operating position. n j

It is apparent that many modications may be made in the shape, number and arrangement of the various elements. Itis apparent, for eX- ample, that the rod I6 may be of shorter length and that a rod of other material may extend through the casing. Furthermore, the rod I6 may be xed in position instead of being adjust- -v able. Accordingly, I desireonly such limitationsy to be imposed on the following'claims as are necessitated by the prior art.

I claim as my invention:

1. A cathode for a cathode-ray tube in which a concentrated cathode-ray beam is produced and then subjected to deflection, said cathode comprising a central rod of aluminum and a cylinder of metal of higher Work function surrounding said rod of aluminum, the rim of said cylinder projecting beyond the face of said rod. 2. A cathode for a cathode-ray tube comprising a central'rod of aluminum and a cylinder of metal of higher Work function surrounding said rod of aluminum, the rim of said cylinder projeoting beyond the face of said rod, said rod extending above the portion of the cylinder immediately surrounding the rod.

3. A cathode for a cathode ray tube comprisinga central rod'of aluminum and a surroundingcylinder of steel, said cylinder having an edge projecting beyond the face of said aluminum rod.

FRANK R. BENEDICT. 

